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[BTI] Muxponder (MXP) client port loops traffic without loopback configured



Article ID: KB34679 KB Last Updated: 12 Jul 2019Version: 1.0

This article describes an issue where a BTI7000 series Muxponder (MXP) module client port, which utilizes GFP-T datapath, loops traffic despite no terminal loopback configured.


This issue can be observed on an MXP module client port that utilizes GFP-T datapath, such as client port configured with port protocol FC4.

The symptom manifests as if the client of the local network element is configured with a terminal loopback, and traffic is looped back towards the far-end network element where it originated; although there is actually no [terminal] loopback configured on the local network element client port.

Refer to the following diagram for clarification:


This issue happens if the FC4 client port of the local NE had been configured with port protocol such as Gigabit Ethernet in GFP-F mode, and had terminal loopback tests in this configuration, prior to it being reconfigured as FC4 port. 

A terminal loopback test on a client port involves enabling terminal loopback, and then disabling terminal loopback when the traffic test is completed. In this issue, ‚Äčterminal loopback is enabled and disabled on the far-end client port back when it was configured as GE GFP-F. The enabling of terminal loopback took affect on both GFP-F and GFP-T datapath for the port. However, the disabling procedure only released the loopback for GFP-F. As a result, when the client port was reconfigured as Fiber Channel (GFP-T), traffic would be loopback when it arrived on this port from crossconnect.


The solution is re-enabling then disabling terminal loopback on the current FC client port to release GFP-T datapath terminal loopback at the local NE. This allows traffic to be forwarded out from the FC4 client port of the local NE as expected.

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